C#迪杰斯特拉算法

C#迪杰斯特拉算法##

网上有许多版本的，自己还是写一个理解点

Dijkstra.cs

public class Dijkstra
{
private List _nodes;
private List _edges;

public Dijkstra()
{
_nodes = new List();
_edges = new List();
}

public void InitWeights(List<Tuple<string, string, double>> weights)
{
_edges = ConvertToEdge(weights);

InitNodes();
}

public List Find(string start, string end)
{
var startNode = GetNodeByName(start);
var endNode = GetNodeByName(end);

if (startNode == null || endNode == null)
{
return new List();
}

var s = _nodes.Where(x => x.Name == start).ToList();
var u = _nodes.Where(x => x.Name != start).ToList();

s.ForEach(x =>
{
x.Weight = 0;
});

u.ForEach(x =>
{
x.Weight = double.PositiveInfinity;
});

while (u.Any())
{
var node = s.Last();

//更新node到x的距离
u.ForEach(x =>
{
var edge = GetEdgeByTwoNode(node, x);

if (edge != null)
{
var weights = node.GetAllWeight() + edge.Weight;

if (weights < x.Weight)
{
x.Weight = weights;
x.Parent = node;
}
}
});

//找出距离最小的
var minNode = u.OrderBy(x => x.Weight).FirstOrDefault();

s.Add(minNode);
u.Remove(minNode);
}

var paths = new Stack();

while (endNode != null)
{
paths.Push(endNode.Name);
endNode = endNode.Parent;
}

//如果路劲中包含起点
if (paths.ToList().Contains(start))
{
return paths.ToList();
}
else
{
return new List();
}
}

private Edge GetEdgeByTwoNode(Node start, Node end)
{
var edge = _edges.FirstOrDefault(x => x.Start == start.Name && x.End == end.Name);

if (edge == null)
{
edge = _edges.FirstOrDefault(x => x.Start == end.Name && x.End == start.Name);
}

return edge;
}

///

/// 将权值转换成边
///

///
private List ConvertToEdge(List<Tuple<string, string, double>> weights)
{
var edges = new List();

weights.ForEach(weight =>
{
edges.Add(new Edge()
{
Start = weight.Item1,
End = weight.Item2,
Weight = weight.Item3
});
});

return edges;
}

///

/// 根据名字获取节点
///

///
///
private Node GetNodeByName(string nodeName)
{
return _nodes.FirstOrDefault(x => x.Name == nodeName);
}

///

/// 初始化点
///

private void InitNodes()
{
_edges.ForEach(weight =>
{
if (_nodes.All(x => x.Name != weight.Start))
{
_nodes.Add(new Node()
{
Name = weight.Start
});
}

if (_nodes.All(x => x.Name != weight.End))
{
_nodes.Add(new Node()
{
Name = weight.End
});
}
});
}
}

Edge.cs

//表示一条边，从Start到End的权值为多少
internal class Edge
{
public string Start
{
get; set;
}

public string End
{
get; set;
}

public double Weight
{
get; set;
}
}

Node.cs

internal class Node
{
public string Name
{
get; set;
}

public Node Parent
{
get; set;
}

///

/// 该节点到起点的最短距离
///

public double Weight
{
get; set;
}

public double GetAllWeight()
{
var allWeight = 0d;

var node = this;

do
{
allWeight += node.Weight;

node = node.Parent;

} while (node != null);

return allWeight;
}
}

使用如下

static void Main(string[] args)
{
var weights = new List<Tuple<string, string, double>>()
{
new Tuple<string,string,double>("A","B",12),
new Tuple<string,string,double>("A","F",16),
new Tuple<string,string,double>("A","G",14),
new Tuple<string,string,double>("B","F",7),
new Tuple<string,string,double>("B","C",10),
new Tuple<string,string,double>("G","F",9),
new Tuple<string,string,double>("G","E",8),
new Tuple<string,string,double>("F","C",6),
new Tuple<string,string,double>("F","E",2),
new Tuple<string,string,double>("C","D",3),
new Tuple<string,string,double>("C","E",5),
new Tuple<string,string,double>("E","D",4),
};

var dij = new Dijkstra();

dij.InitWeights(weights);

var path = dij.Find("D", "G");

path.ForEach(Console.WriteLine);
}